Peptides, peptidomimetics and small molecule inhibitors of the Epstein-Barr virus mediated fusion and entry process

ABSTRACT

Disclosed are compositions and methods for modulating Epstein-Barr virus (EBV) infection in a patient. The compositions may include peptides or peptidomimetics that are related to gp42 and function to inhibit EBV-mediated membrane fusion.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority under 35 U.S.C. §119(e) to U.S. provisional application No. 60/943,724, filed on Jun. 13, 2007, and to U.S. provisional application No. 60/951,304, filed on Jul. 23, 2007, the contents of which are incorporated herein by reference in their entireties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with U.S. Government Support from the following agency: NIH, Grant No. CA93444 and Grant No. CA117794. The U.S. Government has certain rights in the invention.

BACKGROUND

Epstein-Barr virus (EBV) is a member of the human herpesviruses, all of which are membrane enveloped viruses that utilize multiple glycoproteins to enter cells. More than 90% of the adult population is sero-positive for EBV, which efficiently infects both epithelial and B cells, the latter providing the latency reservoir. Acute EBV infection acquired in adolescence or adulthood can cause infectious mononucleosis, accompanied by a proliferation of B cells. In addition, both cell types can develop tumors that are directly linked to EBV such as nasopharyngeal carcinoma and Burkitt's lymphoma. Other malignancies also connected to EBV include post-transplant lymphoproliferative disorder (PTLD) as well as oral hairy leukoplakia and B cell lymphomas of the central nervous system prevalent in AIDS and immunosuppressed individuals. The medical relevance of EBV makes it an important subject of study, especially understanding the mechanism by which the virus enters its two target cell types.

The minimum requirement for membrane fusion to occur with epithelial cells the coexpression of EBV envelope glycoproteins gH, gL, and gB. EBV additionally requires the gp42 protein for entry into B cells (Haan et al., 2001, Virology 290:106-14; Li et al., 1995. J. Virol. 69:3987-94; and McShane et al., 2004, PNAS USA 101:17474-9, incorporated by reference herein in their entireties). EBV gp42 binds major histocompatibility complex (MHC) class II proteins expressed on B cells to trigger viral-cell membrane fusion. A soluble gp42-Fc chimeric protein can stimulate the entry of a gp42-null virus into B cells and likewise, the addition of baculovirus-produced, soluble gp42 to cells transfected with gH, gL, and gB allows membrane fusion to occur with B cells (Kirschner et al., 2006, J. Virol. 80:9444-54; and Wang et al., 1998, J. Virol. 72:5552-8, incorporated by reference herein in their entireties). However, membrane fusion with epithelial cells is actually inhibited by the presence of gp42 for both virus infection and a cell:cell fusion assay. Increasing levels of inhibition occur as exogenous soluble gp42 is added in a cell:cell fusion assay, beginning in the low nanomolar concentration range.

Nearly all herpesviruses contain a gH/gL complex, which serves an indispensable role in membrane fusion and infection. EBV gH requires the presence of gL in order for EBV gH to fold properly and be transported to the cell membrane, and both EBV gL and the related varicella-zoster virus (VZV) gL proteins function effectively in mediating the folding and expression of EBV gH protein. It has also been established that EBV gH/gL exists as a non-covalently associated heterodimer complex in 1:1 subunit ratio.

EBV and other herpesviruses use a multicomponent system for membrane fusion, which is different from other known viral fusion systems that utilize a single fusion protein. The presence or absence of EBV gp42 appears to act as a switch for virus entry into B cells or epithelial cells, respectively, and its interaction with gH/gL is a fundamental feature in EBV-mediated membrane fusion.

There is a need in the art for a better understanding of the interactions between EBV gH/gL and gp42 in the virus entry mechanism. Variants of gp42 that inhibit EBV-mediated cell fusion may provide new peptide-based drugs for treating and prevented conditions and diseases associated with EBV infection.

SUMMARY

Disclosed are peptide-based compounds (e.g., peptides or peptidomimetics) and other small molecules that function to modulate Epstein-Barr virus (EBV) infection. In particular, the peptides, peptidomimetics, and other small molecules function to inhibit EBV-mediated membrane fusion with target cells. For example, the disclosed peptides, peptidomimetics, and other small molecules function may interfere with EBV-mediated membrane fusion with epithelial cells, B-cells, or both. The peptides, peptidomimetics, and other small molecules function typically have a relatively low molecular weight (e.g., less than about 10 K_(d), preferably less than about 7.5 dD, more preferably less than about 5 K_(d), most preferably less than about 1 K_(d)). Typically, the peptides and peptidomimetics are based on the EBV fusion protein gp42. In some embodiments, the peptides and peptidomimetics have a peptide structure corresponding to a variant or mutant gp42 which does not include a lectin domain. The peptides and peptidomimetics may have one or more functional or biological activities associated with gp42. The peptides, peptidomimetics, and other small molecules may be formulated as pharmaceutical compositions for treating and preventing conditions and diseases associated with EBV infection, such as acute infectious mononucleosis, B-cell lymphomas, other lymphoproliferative diseases, and epithelial cancers associated with EBV.

The disclosed peptides may comprise or consist of a fragment of gp42 which does not include the lectin domain and functions to inhibit EBV-mediated fusion to target cells at concentrations of less than about 100 micromolar (preferably less than about 10 micromolar, 1 micromolar, 100 nanomolar, 50 nanomolar, 20 nanomolar, or most preferably less than about 10 nanomolar). Target cells may include B-cells, epithelial cells or both. At the disclosed concentrations, the peptides may inhibit at least about 20% of EBV fusion with target cells (preferably at least about 50%, more preferably at least about 70%, and most preferably at least about 90% of EBV fusion with target cells).

The peptides may bind to gH, gL and/or a gH/gL complex with a relative high affinity. In some embodiments, the pharmaceutical composition comprises a fragment of EBV gp42, where the fragment binds a gH/gL complex with a K_(d) of less than about 1 micromolar (more preferably with a K_(d) of less than about 500 nanomolar, 100 nanomolar, 20 nanomolar, or most preferably with a K_(d) of less than about 10 nanomolar). In further embodiments, the gp42 fragment binds the gH/gL complex and may have a K_(d) within a range of about 1-20 nanomolar. A fragment may include one or more contiguous amino acid sequences of gp42 (e.g., a contiguous amino acid sequence of gp42 having at least (or no more than) 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100 amino acids). A fragment of gp42 may include an N-terminal truncation, a C-terminal truncation, or both (e.g., a 10, 20, 30, or 35 amino acid truncation at the N-terminus and/or a 20, 40, 80, or 140 amino acid truncation at the C-terminus). Preferably, the gp42 fragment inhibits fusion of EBV with B cells, epithelial cells, or both.

The peptides and peptidomimetics may be formulated as a pharmaceutical composition for treating or preventing conditions associated with EBV infection as disclosed herein. The compositions may include a carrier, diluent, or excipient.

The pharmaceutical composition may comprise a fragment of gp42 or a peptidomimetic thereof, where the fragment is present at a concentration effective for inhibiting EBV infection in target cells (e.g., by inhibiting EBV-mediated membrane fusion with target cells). In some embodiments, the pharmaceutical composition may comprise an effective concentration of the gp42 fragment or peptidomimetic for inhibiting of at least about 20% of EBV fusion with B cells, and preferably at least about 50% of EBV fusion with B cells. In further embodiments, the pharmaceutical composition may comprise a fragment of gp42, where the fragment is present at a concentration effective for inhibiting at least about 50% of EBV fusion with epithelial cells, and preferably at least about 90% of EBV fusion with epithelial cells.

In some embodiments, the pharmaceutical composition may comprise an effective concentration of a gp42 fragment for inhibiting EBV fusion with a target cell, the compound comprising a peptide which comprises or consists of gp42 amino acids 36-81 or a peptide variant thereof having at least about 95% sequence identity to gp42 amino acids 36-81, where the variant has gH/gL complex binding activity. In other embodiments, the pharmaceutical composition may comprise an effective concentration of a compound for inhibiting EBV fusion with a target cell, the compound comprising a peptide which comprises or consists of gp42 amino acids 36-65 or a peptide variant thereof having at least about 95% sequence identity to gp42 amino acids 36-65, where the variant has gH/gL complex binding activity. In further embodiments, the pharmaceutical composition comprises an effective concentration of a compound for inhibiting EBV fusion with a target cell, the compound comprising or consisting of a peptidomimetic or a peptide of less than about fifty amino acid residues and having the structure and function of gp42 amino acids 36-81, the peptidomimetic or peptide binding specifically to gH/gL complex. In even further embodiments, the pharmaceutical composition comprises an effective concentration of a compound for inhibiting EBV fusion with a target cell, the compound comprising or consisting of a peptidomimetic or a peptide of less than about fifty amino acid residues and having the structure and function of gp42 amino acids 36-65, the peptidomimetic or peptide binding specifically to gH/gL complex.

Preferably, the pharmaceutical compositions comprises a compound (e.g., a peptide or peptidomimetic) which binds gH, gL, and/or a gH/gL complex with a K_(d) of less than about 1 micromolar (more preferably with a K_(d) of less than about 500 nanomolar, 100 nanomolar, 50 nanomolar, 20 nanomolar, or most preferably with a K_(d) of less than about 10 nanomolar).

Also disclosed are methods of inhibiting EBV infection in a patient in need thereof comprising administering to the patient the pharmaceutical compositions disclosed herein. The disclosed methods may include treatment or prevention methods that include inhibiting EBV infection of B cells, epithelial cells, or both (e.g., by inhibiting EBV-mediated membrane fusion).

Also disclosed are screening methods for identifying inhibitors of EBV fusion with a target cell. The methods may include contacting a test compound with a peptide comprising or consisting of a gp42 variant or a peptidomimetic thereof and identifying a compound that binds to the peptide, thereby identifying a compound for inhibiting EBV fusion with the target cell. A gp42 variant of the screening method may comprise or consist of a fragment of gp42. In some embodiments, a gp42 comprises or consists of amino acid sequence 36-81 of gp42 or an amino acid sequence having at least about 95% sequence identity to gp42 amino acid sequence 36-81 where the variant has gH/gL complex binding activity. In other embodiments, a gp42 variant comprises or consists of amino acid sequence 36-65 of gp42 or an amino acid sequence having at least about 95% sequence identity to gp42 amino acid sequence 36-65 where the variant has gH/gL complex binding activity. The screening methods further may include demonstrating that the identified compound inhibits binding of gp42 to the gH/gL complex or demonstrating that the identified compound inhibits EBV-mediated membrane fusion with B-cells, epithelial cells, or both.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of gp42 mutants, fusion assay and CELISA data. (A) Map of EBV gp42 amino-terminal ectodomain residues 30-100 depicting mutant constructs of either 5-residue and longer deletions or single residue substitutions. Individual residues that were mutated to alanine are shown in bold. Italics highlight predicted glycosylation sites. Putative cleavage and crystal (Xtal) dimerization sites are indicated by dotted lines from above. Soluble gp42 starts at residue 33 and is indicated by an angled arrow. Important functional domains designated NT1 and NT2 are represented by double arrows and peptides derived from gp42 are shown below. The “core” binding residues based on concordance between activity in fusion and binding soluble gH/gL in CELISA are below black boxes. Gray lines depict the peptides used in this study. (B) Cell-cell fusion assay relative luciferase activity measured using CHO cells transfected with gH, gL, gB, and wild-type or mutant gp42, and overlaid with B cells (bar graph). Surface expression of gp42 is measured by CELISA using monoclonal F-2-1 antibody, secondary biotinylated-anti-mouse-IgG antibody, tertiary streptavidin-HRP, and TMB substrate (line graph). Color development measured by absorbance at 370mm. Data shown are averages of at least 3 independent experiments with wild-type gp42 luciferase activity and expression set at 100%, and standard deviations are represented by the error bars.

FIG. 2 illustrates binding of gp42 mutants with transfected gH/gL in co-immunoprecipitations and soluble gH/gL in CELISA. (A and B) SDS-PAGE Western blots of wild-type and mutant gp42 expressed in CHO cells using rabbit polyclonal PB1114 anti-gp42 antibody at 1:1000 for detection reveal gp42 levels in immunoprecipitations using either F-2-1 anti-gp42 antibody or E1D1 anti-gH/gL antibody as labeled. Samples are from the same transfection and were simultaneously run in non-adjacent lanes. (C) CELISA-based quantitative measurements of soluble gH/gL binding to transfected gp42. Detection of bound gH/gL is carried out with E1D1 anti-gH/gL antibody, as in CELISA in FIG. 1B. Data shown is a representative example of 3 or more independent experiments, and error bars represent standard deviations across triplicate measurements within an experiment. Data for all mutants is summarized in Table 1.

FIG. 3 demonstrates equilibrium binding of gp42 peptides to soluble gH/gL measured by fluorescence polarization. (A) Binding between soluble gH/gL and FITC-labeled gp42-peptide 36-81 shows increased fluorescence polarization signal as the concentration of soluble gH/gL is increased. The concentration of peptide was kept constant at 10 nM, and 50% of binding occurs at 5.1±1.1 nM gH/gL. (B-D) Fluorescence polarization measurements using constant 10 nM concentrations of soluble gH/gL and 10 nM FITC-labeled gp42-peptide 36-81 with added competitor (100% corresponds to no competitor): (B) soluble gp42 protein, EC₅₀ at 8.5±1.0 nM; (C) peptide 36-65, EC₅₀ at 1.5 μM; (D) peptides 36-56, 42-56, and 67-81, EC₅₀ for 42-56 is approximately 152 μM. Competitor is premixed with labeled peptide 36-81, and soluble gH/gL is added to initiate binding.

FIG. 4 illustrates kinetics of FITC-labeled gp42 peptide 36-81 binding soluble gH/gL as determined by fluorescence polarization. The fluorescence polarization signal from FITC-labeled gp42 peptide 36-81 was monitored at time points immediately after mixing samples. (A) Peptide 36-81 binding to soluble gH/gL, each present at 10 nM concentration. Binding is nearly complete by 10 min with a rate constant of 0.908±0.039 min⁻¹. (B) Dissociation of premixed 10 nM gH/gL and 10 nM FITC-labeled gp42-peptide 36-81 is observed by adding soluble gp42 at 1 μM. Half-life of the gH/gL/peptide complex is 9.86±0.6 min.

FIG. 5 illustrates peptide from gp42 residues 36-81 inhibits epithelial and B-cell membrane fusion. Fusion assay graphs showing concentration-dependent effects of peptide 36-81 on the cell-cell fusion assay. (A) Epithelial cell fusion and (B & C) B-cell fusion; CHO cells were transfected with gH, gL, and gB for (A) and (C), and additionally transfected with gp42 for (B) [far right on graph for (A) is also transfected with gp42]. For (C), soluble gp42 was added to trigger B-cell fusion and demonstrate efficient competition between the peptide and soluble protein. Data shown are the mean of triplicate measurements from at least three independent experiments and error bars indicate standard deviations.

FIG. 6 illustrates shorter gp42-derived peptides tested in epithelial and B-cell. Fusion assay graphs showing (A) no inhibitory effect on epithelial cell fusion with individual gp42-derived peptides tested up to 50 μM final concentration, (B) enhanced inhibition of epithelial cell fusion using simultaneous addition of gp42 peptide 36-65 and 67-81 compared to peptide 36-65 alone, and (C) no restoration of B-cell fusion using transfected gp42 deletion mutants deficient in membrane fusion activity with added peptides, although wild-type soluble gp42 restores fusion. Written above the solid bars are curly brackets outlining the peptides added. Data shown are a representative example from at least two independent experiments and error bars indicate standard deviations.

FIG. 7 illustrates peptide 36-81 inhibition of EBV entry into epithelial cells. A graph of a representative EBV infection assay shows the inhibitory effect of gp42-derived peptide 36-81. Virus was incubated with anti-gH/gL antibody E1D1, soluble gp42, or peptide 36-81 at 20 nM. FACS analysis was used to measure the GFP-expressing cells, and data were transformed to set the medium-only control to 0% infected and the EBV-only control to 100% infected so that each experimental condition demonstrates a fraction of the uninhibited 100% infection. The data shown are representative of at least three independent experiments.

FIG. 8 provides a model of peptide inhibition of EBV membrane fusion apparatus. The N-terminal region of gp42 binds gH/gL with high affinity, and the peptide from gp42 residues 36-81 mimics that interaction. Epithelial cell fusion is inhibited by nanomolar concentrations of gp42 and the peptide 36-81 is sufficient to inhibit at those concentrations as well. B-cell membrane fusion only proceeds when a gp42 lectin domain is supplied in cis with the N-terminal region. Thus, peptide 36-81 is a strong inhibitor of both epithelial and B-cell membrane fusion.

DETAILED DESCRIPTION

The subject matter disclosed herein is described using several definitions, as set forth below and throughout the application.

Unless otherwise noted, the terms used herein are to be understood according to conventional usage by those of ordinary skill in the relevant art. In addition to the definitions of terms provided below, it is to be understood that as used in the specification, embodiments, and in the claims, “a”, “an”, and “the” can mean one or more, depending upon the context in which it is used.

As used herein, “about,” “approximately,” “substantially,” and “significantly” will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which they are used. If there are uses of the term which are not clear to persons of ordinary skill in the art given the context in which it is used, “about” or “approximately” will mean up to plus or minus 10% of the particular term and “substantially” and “significantly” will mean more than plus or minus 10% of the particular term.

As used herein, the term “patient” may be used interchangeable with the term “subject” and means an animal, which may be a human or non-human animal, in need of treatment. Non-human animals may include dogs, cats, horses, cows, pigs, sheep, and the like.

A “patient in need thereof” may include a patient infected with Epstein-Barr virus. A patient in need thereof may include a patient diagnosed with one or more of the following diseases or disorders: infectious mononucleosis, lymphoma (including B-cell lymphomas and T-cell lymphomas), carcinoma (e.g., nasopharyngeal carcinoma), and hairy leukoplakia. A patient in need thereof may include a patient diagnosed with Burkitt's lymphoma, non-Hodgkin's lymphoma, or Hodgkin's lymphoma.

As used herein, the phrase “therapeutically effective amount” shall mean that dosage of an active agent that provides the specific pharmacological response for which the active agent is administered in a significant number of subjects in need of such treatment. A therapeutically effective amount of an active agent that is administered to a particular subject in a particular instance will not always be effective in all instances for treating the conditions/diseases described herein, even though such dosage is deemed to be a therapeutically effective amount in particular instances by those of skill in the art.

As used herein, a “variant” or “mutant” refers to a polypeptide or a polynucleotide molecule having an amino acid sequence or nucleic acid sequence, respectively, that differs from a reference polypeptide or polynucleotide molecule, respectively. A variant or mutant may have one or more insertions, deletions, or substitutions of an amino acid residue or nucleotide residue relative to a reference molecule. A variant or mutant may include a fragment of a reference polypeptide. For example, a gp42 variant polypeptide has one or more insertions, deletions, or substitution of at least one amino acid residue relative to the gp42 polypeptide.

As described herein, variants, mutants, or fragments (e.g., a gp42 variant, mutant, or fragment polypeptide) may have 99%, 98%, 97%, 96%, 95%, 94%, 93%, 92%, 91%, 90%, 80%, 70%, 60%, or 50% amino acid sequence identity (or nucleic acid sequence identity) relative to a reference molecule (e.g., relative to the gp42 polypeptide). “Percentage sequence identity” may be determined by aligning two sequences using the Basic Local Alignment Search Tool available at the NBCI website (i.e., “bl2seq” as described in Tatiana A. Tatusova, Thomas L. Madden (1999), “Blast 2 sequences—a new tool for comparing protein and nucleotide sequences”, FEMS Microbiol Lett. 174:247-250, incorporated herein by reference in its entirety)).

The variants, mutants, or fragments described herein may have one or functional or biological activities exhibited by a reference polypeptide (e.g., one or more functional or biological activities exhibited by gp42). Variants, mutants, or fragments may bind to gH, gL, or both to form a tripartite complex. Variants, mutants, or fragments described herein may compete with gp42 for binding to one or more of gH, gL, or a gH/gL complex. Variants, mutants, or fragments may inhibit EBV infection of target cells such as B-cells, epithelial cells, or both (e.g., by inhibiting EBV-mediated membrane fusion to target cells such as B-cells, epithelial cells, or both).

As disclosed herein, a fragment comprises or consists of a contiguous portion of an amino acid sequence of a full-length polypeptide. For example, a fragment may comprise or consist of a 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100 contiguous amino acid sequence of a full-length polypeptide. A fragment of gp42 may comprise or consist of a 30-100 contiguous amino acid sequence of gp42 (or in some embodiments a 40-100 contiguous amino acid sequence of gp42, or a 46-100 contiguous amino acid sequence of gp42). In some embodiments, a fragment of gp42 may comprise or consist of amino acid sequence 36-81 of gp42 or amino acid sequence 36-65 of gp42. A fragment may include an N-terminal truncation, a C-terminal truncation, or both. In some embodiments, a fragment of gp42 does not comprise the entire lectin domain of gp42 (e.g., the fragment has a deletion of one or more amino acids within the lectin domain of gp42, preferably 10 or more N-terminal amino acids). In further embodiments, a fragment of gp42 does not comprise a C-terminal amino acid sequence of gp42 (e.g., where amino acid sequence 82-223 of gp42 or amino acid sequence 100-223 of gp42 are deleted).

The polypeptides disclosed herein may include peptidomimetics. As disclosed herein, a peptidomimetic is a peptide equivalent characterized as retaining the polarity, three dimensional size and functionality (bioactivity) of its peptide equivalent but where the peptide bonds have been replaced (e.g., by more stable linkages which are more resistant to enzymatic degradation by hydrolytic enzymes). Generally, the bond which replaces the amide bond conserves many of the properties of the amide bond (e.g., conformation, steric bulk, electrostatic character, and possibility for hydrogen bonding). A general discussion of prior art techniques for the design and synthesis of peptidomimetics is provided in “Drug Design and Development”, Chapter 14, Krogsgaard, Larsen, Liljefors and Madsen (Eds) 1996, Horwood Acad. Pub, the contents of which are incorporated herein by reference in their entirety. Suitable amide bond substitutes include the following groups: N-alkylation (Schmidt, R. et. al., Int. J. Peptide Protein Res., 1995, 46, 47), retro-inverse amide (Chorev, M. and Goodman, M., Acc. Chem. Res, 1993, 26, 266), thioamide (Sherman D. B. and Spatola, A. F. J. Am. Chem. Soc., 1990, 112, 433), thioester, phosphonate, ketomethylene (Hoffman, R. V. and Kim, H. O. J. Org. Chem., 1995, 60, 5107), hydroxymethylene, fluorovinyl (Allmendinger, T. et al., Tetrahydron Lett., 1990, 31, 7297), vinyl, methyleneamino (Sasaki, Y and Abe, J. Chem. Pharm. Bull. 1997 45, 13), methylenethio (Spatola, A. F., Methods Neurosci, 1993, 13, 19), alkane (Lavielle, S. et. al., Int. J. Peptide Protein Res., 1993, 42, 270) and sulfonamido (Luisi, G. et al. Tetrahedron Lett. 1993, 34, 2391), which all are incorporated herein by reference in their entireties. The polypeptides disclosed herein may include peptidomimetic equivalents of the disclosed gp42 variants, mutants, and fragments.

The pharmaceutical compositions disclosed herein may include a carrier, excipient, or diluent (i.e., agents), which are nontoxic to the cell or mammal being exposed thereto at the dosages and concentrations employed. Often a physiologically acceptable agent is an aqueous pH buffered solution. Examples of physiologically acceptable carriers include buffers such as phosphate, citrate, and other organic acids; antioxidants including ascorbic acid; low molecular weight (less than about 10 residues) polypeptide; proteins, such as serum albumin, gelatin, or immunoglobulins; hydrophilic polymers such as polyvinylpyrrolidone; amino acids such as glycine, glutamine, asparagine, arginine or lysine; monosaccharides, disaccharides, and other carbohydrates including glucose, mannose, or dextrins; chelating agents such as EDTA; sugar alcohols such as mannitol or sorbitol; salt-forming counterions such as sodium; and/or nonionic surfactants such as TWEEN™, polyethylene glycol (PEG), and PLURONICS™.

The pharmaceutical compositions disclosed herein may include additional therapeutic agents or prophylactic agents against EBV infection. Additional pharmaceutical agents may include glucocorticoids (e.g., prednisone), antiviral agents (e.g., acyclovir, desciclovir, ganciclovir, interferon-α, interferon-γ, adenine arabinoside, and phosphonoacetic acid), and immunoglobulins, such as anti-EBV immunoglobulins conjugated to therapeutic agents (e.g., anti-cancer drugs or radionuclides) or immune globulins for intravenous injection such as those sold under trade name Gammagard®).

Illustrative Embodiments

The following embodiments are illustrative and are not intended to limit the scope of the disclosed subject matter.

Embodiment 1

A pharmaceutical composition comprising an effective concentration of a compound for inhibiting EBV fusion with a target cell, the compound comprising a peptide which comprises or consists of gp42 amino acids 36-81 or a peptide variant thereof having at least about 95% sequence identity to gp42 amino acids 36-81 wherein the variant has gH/gL complex binding activity.

Embodiment 2

A pharmaceutical composition comprising an effective concentration of a compound for inhibiting EBV fusion with a target cell, the compound comprising a peptide which comprises or consists of gp42 amino acids 36-65 or a peptide variant thereof having at least about 95% sequence identity to gp42 amino acids 36-65, wherein the variant has gH/gL complex binding activity.

Embodiment 3

A pharmaceutical composition comprising an effective concentration of a compound for inhibiting EBV fusion with a target cell, the compound comprising or consisting of a peptidomimetic or a peptide of less than about fifty amino acid residues and having the structure and function of gp42 amino acids 36-81, the peptidomimetic or peptide binding specifically to gH/gL complex.

Embodiment 4

A pharmaceutical composition comprising an effective concentration of a compound for inhibiting EBV fusion with a target cell, the compound comprising or consisting of a peptidomimetic or a peptide of less than about fifty amino acid residues and having the structure and function of gp42 amino acids 36-65, the peptidomimetic or peptide binding specifically to gH/gL complex.

Embodiment 5

The pharmaceutical composition of any of embodiments 1-4, wherein the target cell is a B cell and the concentration of the compound is effective for inhibiting at least about 20% of EBV fusion, preferably at least about 50% of EBV fusion.

Embodiment 6

The pharmaceutical composition of any of embodiments 1-4, wherein the target cell is an epithelial cell and the concentration of the compound is effective for inhibiting about 50% of EBV fusion, preferably at least about 90% of EBV fusion.

Embodiment 7

The pharmaceutical composition of embodiment 1 or 2, wherein the peptide or peptide variant binds the gH/gL complex with a K_(d) of less than about 1 micromolar.

Embodiment 8

The pharmaceutical composition of embodiment 1 or 2, wherein the peptide or peptide variant binds the gH/gL complex with a K_(d) of less than about 500 nanomolar.

Embodiment 9

The pharmaceutical composition of embodiment 1 or 2, wherein the peptide or peptide variant binds the gH/gL complex with a K_(d) of less than about 100 nanomolar.

Embodiment 10

The pharmaceutical composition of embodiment 1 or 2, wherein the peptide or peptide variant binds the gH/gL complex with a K_(d) of less than about 20 nanomolar.

Embodiment 11

The pharmaceutical composition of embodiment 3 or 4, wherein the peptidomimetic or peptide binds to the gH/gL complex with a K_(d) of less than about 1 micromolar.

Embodiment 12

The pharmaceutical composition of embodiment 3 or 4, wherein the peptidomimetic or peptide binds to the gH/gL complex with a K_(d) of less than about 500 nanomolar.

Embodiment 13

The pharmaceutical composition of embodiment 3 or 4, wherein the peptidomimetic or peptide binds to the gH/gL complex with a K_(d) of less than about 100 nanomolar.

Embodiment 14

The pharmaceutical composition of embodiment 3 or 4, wherein the peptidomimetic or peptide binds to the gH/gL complex with a K_(d) of less than about 20 nanomolar.

Embodiment 16

A pharmaceutical composition comprising a fragment of EBV gp42, wherein the fragment binds a gH/gL complex with a K_(d) of less than about 1 micromolar and inhibits fusion of EBV with B cells.

Embodiment 17

The pharmaceutical composition of embodiment 16, wherein the fragment binds the gH/gL complex with a K_(d) of less than about 500 nanomolar.

Embodiment 18

The pharmaceutical composition of embodiment 16, wherein the fragment binds the gH/gL complex with a K_(d) of less than about 100 nanomolar.

Embodiment 19

The pharmaceutical composition of embodiment 16, wherein the fragment binds the gH/gL complex with a K_(d) of less than about 20 nanomolar.

Embodiment 20

The pharmaceutical composition of embodiment 16, wherein the fragment binds the gH/gL complex with a K_(d) of less than about 10 nanomolar.

Embodiment 21

The pharmaceutical composition of embodiment 16, wherein the fragment binds the gH/gL complex with a K_(d) of about 1-20 nanomolar.

Embodiment 22

The pharmaceutical composition of embodiment 16, wherein the fragment is present at a concentration effective for inhibiting at least about 20% of EBV fusion with B cells, preferably at least about 50% of EBV fusion with B cells.

Embodiment 23

The pharmaceutical composition of embodiment 16, wherein the fragment is present at a concentration effective for inhibiting at least about 50% of EBV fusion with epithelial cells, preferably at least about 90% of EBV fusion with epithelial cells.

Embodiment 24

The pharmaceutical composition of embodiment 16, wherein the fragment consists of a 30-100 contiguous amino acid sequence of gp42.

Embodiment 25

The pharmaceutical composition of embodiment 16, wherein the fragment consists of a 40-100 contiguous amino acid sequence of gp42.

Embodiment 26

The pharmaceutical composition of embodiment 16, wherein the fragment consists of a 46-100 contiguous amino acid sequence of gp42.

Embodiment 27

The pharmaceutical composition of any of embodiments 16-26, wherein the fragment comprises amino acid sequence 36-81 of gp42.

Embodiment 28

The pharmaceutical composition of any of embodiments 16-26, wherein the fragment comprises amino acid sequence 36-65 of gp42.

Embodiment 29

The pharmaceutical composition of any of embodiments 16-28, wherein the fragment does not comprise the lectin domain of gp42.

Embodiment 30

The pharmaceutical composition of any of embodiments 16-29, wherein the fragment does not comprise amino acid sequence 82-223 of gp42.

Embodiment 31

The pharmaceutical composition of any of embodiments 16-30, wherein the fragment does not comprise amino acid sequence 100-223 of gp42.

Embodiment 32

The pharmaceutical composition of any of embodiments 1-28, further comprising a carrier or excipient.

Embodiment 33

A method of inhibiting EBV infection in a patient in need thereof comprising administering to the patient the pharmaceutical composition of any of embodiments 1-32.

Embodiment 34

A method of inhibiting EBV infection in a patient in need thereof comprising administering a pharmaceutical composition comprising an effective concentration of a peptide comprising or consisting of gp42 amino acids 36-81 or a peptide variant thereof having at least about 95% sequence identity to gp42 amino acids 36-81 wherein the variant has gH/gL complex binding activity.

Embodiment 35

The method of embodiment 34, wherein the composition inhibits at least about 20% of EBV fusion with B cells, and preferably at least about 50% of EBV fusion with B cells.

Embodiment 36

The method of embodiment 34 or 35, wherein the composition inhibits at least about 90% of EBV fusion with epithelial cells.

Embodiment 37

The method of any of embodiments 34-37, wherein the peptide comprises or consists of gp42 amino acids 36-65 or a peptide variant thereof having at least about 95% sequence identity to gp42 amino acids 36-65 wherein the variant has gH/gL complex binding activity.

Embodiment 38

A method for screening for inhibitors of EBV fusion with a target cell, the method comprising contacting a test compound with a peptide comprising or consisting of gp42 amino acids 36-81 or a peptide variant thereof having at least about 95% sequence identity to gp42 amino acids 36-81 wherein the variant has gH/gL complex binding activity; and identifying a compound that binds to the peptide or peptide variant thereby identifying a compound for inhibiting EBV fusion with the target cell.

Embodiment 39

A method for screening for inhibitors of EBV fusion with a target cell, the method comprising contacting a test compound with a peptide comprising or consisting of gp42 amino acids 36-65 or a peptide variant thereof having at least about 95% sequence identity to gp42 amino acids 36-65 wherein the variant has gH/gL complex binding activity; and identifying a compound that binds to the peptide or peptide variant thereby identifying a compound for inhibiting EBV fusion with the target cell.

Embodiment 40

A method for screening for inhibitors of EBV fusion with a target cell, the method comprising contacting a test compound with a peptidomimetic or peptide of less than about 50 amino acid residues and having the structure and function of gp42 amino acids 36-81, the peptidomimetic or peptide binding specifically to gH/gL complex; and identifying a compound that binds to the peptidomimetic or peptide thereby identifying a compound for inhibiting EBV fusion with the target cell.

Embodiment 41

A method for screening for inhibitors of EBV fusion with a target cell, the method comprising contacting a test compound with a peptidomimetic or a peptide of less than about 50 amino acid residues and having the structure and function of gp42 amino acids 36-65, the peptidomimetic or peptide binding specifically to gH/gL complex; and identifying a compound that binds to the peptidomimetice or peptide thereby identifying a compound for inhibiting EBV fusion with the target cell.

Embodiment 42

The method of any of embodiments 38-41 wherein the identified compound inhibits binding of gp42 to the gH/gL complex.

EXAMPLES

The following examples are illustrative and are not intended to limit the disclosed subject matter.

Materials and Methods

Cells and Proteins. High Five insect cells (BTI-TN-5B1-4, Invitrogen) were grown in shaker flasks in Excell-405 medium (JRH Biosciences). Sf9 insect cells (Invitrogen) were grown in shaker flasks in Sf900 medium (Gibco).

All media for mammalian cell growth were made complete by supplementing with 10% FetalPlex animal serum complex (Gemini Bio-Products) and 1 % penicillin-streptomycin (BioWhittaker), and all mammalian cells were grown in 75-cm² cell culture flasks (Corning). Mammalian epithelial cells were human embryonic kidney 293 cells that express SV40 large T antigen (ATCC, Manassas, Va.) and modified to stably express T7 RNA polymerase under selection of 100 μg/ml zeocin in complete Dulbecco modified Eagle medium (BioWhittaker), which is known as line 14 as described previously (Omerovic et al., 2005. J. VIROL. 79:12408-15, incorporated by reference herein in its entirety). Mammalian B cells were Daudi B lymphocytes that are EBV-positive and express HLA class II and CD21 (ATCC) and modified to stably express T7 RNA polymerase under selection of G418 (700-900 μg/ml) in complete RPMI 1640 medium (BioWhittaker) (Silva et al., 2004. J. VIROL. 78:5946-56, incorporated by reference herein in its entirety). Chinese hamster ovary cells (CHO-K1) were kindly provided by Nanette Susmarski and were grown in complete Ham's F-12 medium (BioWhittaker). Versene (1 mM EDTA in PBS) or trypsin-versene (BioWhittaker) was used to detach adherent cells.

Monoclonal antibodies E1D1 (anti-gH/gL) and F-2-1 (anti-gp42) were gifts generously provided by L. Hutt-Fletcher (Louisiana State University Health Sciences Center, Shreveport) (Balachandran et al., 1987, J. Virol. 61:1125-35; and Strnad et al., 1982, J. Virol. 41:258-64, incorporated by reference herein in their entireties.) Monoclonal antibody 3H3 (anti-gp42) was obtained as previously described (Kirschner et al., 2006, J. Virol. 80:9444-54, incorporated by reference herein in its entirety). Polyclonal anti-gp42 antibody serum PB1114 was used as previously described (McShane et al., 2003, J. Virol. 77:7655-62; and Silva et al., 2004, J. Virol. 78:5946-56, incorporated by reference herein in their entireties). Milligram quantities of antibodies were produced by the Northwestern Monoclonal Antibody Facility and the National Cell Culture Center. For CELISA experiments with soluble gH/gL, monoclonal antibodies 3H3 and E1D1 were purified by a HiTrap Protein G agarose column (Amersham Biosciences), eluted with 0.2 M glycine-HCl pH 2.5, immediately neutralized to pH ˜7 by adding one-tenth volume of 1 M tris pH 9.0. Purity was >95% as demonstrated by SDS-PAGE. Purified antibodies were exchanged into phosphate-buffered saline (PBS) and concentration was determined by absorbance at 280 nm using theoretical extinction coefficient (0.1%) of 1.4 for IgG.

Soluble EBV gp42 and soluble EBV gH/gL were produced and purified as described elsewhere (Kirschner et al., 2006, J. Virol. 80:9444-54, incorporated by reference herein in its entirety). Briefly, gp42 and gH/gL proteins were obtained using the baculovirus expression system in Hi5 and Sf9 insect cells, respectively. Soluble gp42 was purified by cobalt metal affinity chromatography and soluble gH/gL by affinity purification using monoclonal anti-gH/gL antibody E1D1. Gel filtration using a Superdex-200 HR 10/30 analytical column (Amersham Biosciences) provided the final purification in running buffers consisting of PBS or 25 mM tris pH 7.4, 150 mM NaCl (TBS).

Peptides. Synthetic peptides were obtained commercially (EZBiolab) at 95% purity, as determined by high-performance liquid chromatography and mass spectrometry, and used without further purification. Lyophilized peptides were reconstituted in TBS or PBS. Peptide concentration was measured by absorbance at 280 nm using the theoretical 0.1% value. For peptide labeled with fluorescein isothiocyanate (FITC), absorbance maximum at 495 nm for FITC was additionally used to confirm peptide concentration. Peptide 36-81 is N-terminally labeled with FITC and corresponds to gp42 residues 36 to 81 (RVAAAAITWVPKPNVEVWPVDPPPPVNFNKTAEQEYGDKEVKLPHW (SEQ ID NO:1)). Peptide 36-65 corresponds to gp42 residues 36 to 65 (RVAAAAITWVPKPNVEVWPVDPPPPVNFNK (SEQ ID NO:2)) (Kirschner et al., 2006, J. Virol. 80:9444-54, incorporated by reference herein in its entirety). Peptide 36-56 corresponds to gp42 residues 36 to 56 (RVAAAAITWVPKPNVEVWPVD (SEQ ID NO:3)). Peptide 42-56 corresponds to gp42 residues 42 to 56 (ITWVPKPNVEVWPVD (SEQ ID NO:4)). Peptide 67-81 corresponds to gp42 residues 67 to 81 (AEQEYGDKEVKLPHW (SEQ ID NO:5))

Mutants. Mutants were generated using a double-arm polymerase chain reaction (PCR) approach. Mutant primers were generated to incorporate either five residue deletions or single residue changes as well as silent restriction enzyme cutting sites. The first PCR used primers matched to flank the EBV gp42 gene in the pCAGGS.mcs vector (5′ primer p-1 TCCTGGGCAACGTGCTGGTTGTTG (SEQ ID NO:6) and 3′ primer p-2 GCCAGAAGTCAGATGCTCAAGGGG (SEQ ID NO:7)) paired with their complementary directional mutant primer on a wild-type EBV gp42 plasmid template. The PCR “Tails” program was used as follows: (1) 94° C. 2 min (2) 94° C. 15 s (3) 58° C. 1 min (4) 72° C. 90 s (steps 2-4 40 cycles) (5) 72° C. 15 min 6) 4° C. unlimited. PCR products were confirmed by gel electrophoresis and then used as templates with the flanking primers in the second PCR to generate full-length mutant gp42, which was confirmed by gel electrophoresis, cut with EcoR1 and BglII and ligated overnight at 16° C. with vector that had been digested under the same conditions. Ligated products were transformed and selected on ampicillin plates. Colonies were picked and grown overnight to generate mini-preps, which were double digested to confirm the introduction of the mutation. Mini-preps were sequenced and positive clones were then grown in large quantities and isolated in cesium chloride density gradients by ultracentrifugation and sequenced again. Double mutants were generated similarly except mutant gp42 plasmids were used for the first PCR template. The first deletion mutant was used as a template with a different pair of mutant primers to generate the second deletion; e.g. the deletion mutant d37-41/67-71 was created using d37-41 plasmid template with d67-71 mutant primers for the first PCR. Two mutants studied had incorporated inconsequential extra point mutations: K47A gained P48S and d67-71 gained T131. These mutations were detected after sequencing of CsCl preps so new mutants were generated and confirmed to lack any incidental mutations introduced by PCR. Table 1 identifies mutants used in this study. W44A was generated as previously described (Silva et al., 2004, J. Virol. 78:5946-56, incorporated by reference herein in its entirety).

TABLE 1 Activity summary of gp42 deletion mutants.^(a) gH/gL binding Surface Immuno- Mutant Expression Fusion precipitation CELISA Category 1. Functional R30A + + Y ND R32A + + Y ND R36A + + Y ND W44A + + Y ND K47A + + Y ND K47A/P48S + + Y ND E51A + + Y ND d32-36 + + Y + d57-61* + + Y − d62-66 + + Y + Category 2. Fusion impaired, not due to gH/gL binding NT1 d37-41 + − Y + d42-46 + − Y + NT2 d82-86 + − Y + d87-91 + − Y + d92-96 + − Y + Category 3. Fusion impaired due to altered gH/gL binding NT1 d47-51 + − Y +/− d52-56 + − Y − NT2 d67-71 + +/− Y − d72-76 + − Y − d77-81 + − Y +/− NT1 & NT2 d45-89 + − ND − d37-41/d67-71 + − Y − d42-46/d72-76 + − N − d47-51/d77-81 + − N ND d52-56/d77-81 + − ND ND d77-81/d47-51 + − ND − ^(a)Activity is defined as 100% wild-type to 50% (+), between 50% and 25% (+/−), or less than 25% (−). ND is not done. Y is observed by IP Western blot. N is greatly reduced or not observed by IP Western blot. *d57-61 exhibits near wild-type fusion, but reduced interactions with soluble gH/gL.

Transfection. CHO-K1 cells were transfected in Opti-MEM I medium (Gibco) by a uniform protocol using Lipofectamine-2000 (Invitrogen) as previously described (Silva et al., 2004, J. Virol. 78:5946-56, incorporated by reference herein in its entirety). Cells were plated in 6-well format and after 24 h each well received 5 μl Lipofectamine 2000 and various combinations of pCAGGS expression vector containing the gene of interest were used in the following amounts: 0.5 μg for gH; 0.5 μg for gL; 0.8 μg for gB; 0.8 μg for luciferase; 1.7 μg for the pCAGGS vector control (Haan et al., 2001, Virology 290:106-14; and Oda et al., 2000, Virology 276:52-8, incorporated by reference herein in their entireties). In the case of gp42-transfected CHO cells, pCAGGS vector control plasmid was replaced by 1.7 μg gp42 vector. For fusion assays in 1, amounts of DNA were changed to 0.5 μg for gB, 2.0 μg wild-type or mutant gp42, and 1.0 μg each of pCAGGS and EGFP to allow for negative control and visual confirmation of transfection. For immunoprecipitations, gB and luciferase plasmids were excluded and 1.0 μg gH and gL transfected with 2.0 μg of wild-type or mutant gp42. For negative control and visualization, 2.0 μg each of pCAGGS and EGFP were included with no other glycoprotein.

Fusion assay. CHO-K1 cells were transiently transfected as described above. At 12 h post-transfection, the cells were detached by versene, counted either by hand with a hemocytometer or using a Beckman Coulter Z1 particle counter, and 2.0-2.5×10⁵ cells/well in 0.5 ml were transferred to 24-well format, incubated for about 10 min after the addition of peptide and/or soluble proteins (in TBS or PBS without azide), and subsequently overlaid with 0.5 ml target cells, either Daudi B cells or 293-T epithelial cells. For simultaneous surface expression readings by CELISA, 4.0-5.0×10⁴ CHO cells were also plated in 96-wells (described below). To induce fusion, equal or greater numbers of Daudi or 293-T cells were overlaid on CHO cells, and total volume was 1 ml or more per well. Both of the target cells, Daudi and 293-T, used in the fusion assay stably expressed T7 RNA polymerase and were under selection by G418 and zeocin, respectively (Omerovic et al., 2005, J. Virol. 79:12408-15; Silva et al., 2004, J. Virol. 78:5946-56; and Spriggs, et al., 1996, J. Virol. 70:5557-63, incorporated by reference herein in their entireties). After 24 h overlay, cells were washed with PBS and lysed with 100 μl Passive Lysis Buffer (Promega) per well. Luciferase activity was quantified by transferring triplicate 20 μl aliquots of lysed cells to a 96-well opaque plate with clear bottoms (Wallac), and luminescence was measured on a Perkin-Elmer Victor plate reader immediately after adding 100 μl of Luciferase Assay reagent (Promega).

Cell Enzyme-Linked Immunosorbent Assay (CELISA). For testing gp42 mutants binding to soluble gH/gL, 1.7 μg of gp42 (wild-type or mutant) DNA was added with 5 μl Lipofectamine 2000 per well in 6-well format. After 12 h post-transfection, CHO cells were re-plated in 96-well format. After 24 h incubation, the medium was removed, cells were washed with PBS-ABC(PBS with 0.89 g CaCl₂ and 0.89 g MgCl₂*H₂O per 8 L), and soluble gH/gL was added in PBS-ABC with 3% bovine serum albumin (BSA) (Sigma). After 30 min incubation, cells were washed and primary antibody at 50 nM final concentration was added in PBS-ABC with 3% BSA. Cells were fixed for 10 min in PBS with 2% formaldehyde and 0.2% glutaraldehyde and then blocked with 3% BSA in PBS-ABC. Biotinylated anti-mouse-IgG at 1:500 was added as the secondary antibody, followed by streptavidin-HRP at 1:20,000. 3,3′,5,5′-Tetramethylbenzidine (TMB) substrate (Sigma) was added and quantitative colorimetric measurement was performed at 370 nm using a Victor plate reader, typically achieving a high signal over background measurement by 30 to 60 min. Background measurements were obtained from negative control wells that omitted the transfected glycoprotein expression plasmid and/or omitted primary antibody. Surface expression of transfected gp42 was measured using 50 nM 3H3 antibody, and binding of soluble gH/gL to transfected gp42 was measured using 50 nM E1D1 antibody. Percent soluble gH/gL binding to gp42 was determined by dividing the background-subtracted binding of soluble gH/gL by the background-subtracted surface expression for each gp42 mutant. The wild-type gp42 sample binding to soluble gH/gL was then set to 100% and gp42 mutants normalized to that value. For measurement of cell surface expression simultaneous with fusion assays, CHO cells transfected for fusion were also plated in 96-well format 12 h post-transfection and CELISA was performed 24 h later. Primary antibody was F-2-1 hybridoma supernatant used at a dilution of 1:150.

Immunoprecipitation (IP). CHO cells were transfected with plasmids encoding EBV gH, gL, and either wild-type or mutant gp42. Opti-MEM medium was removed 12 h post-transfection and replaced with complete Ham's F-12 medium. After 24 h incubation, cells were detached with versene, counted, washed twice in PBS, and lysed as previously described (Silva et al., 2004, J. Virol. 78:5946-56, incorporated by reference herein in its entirety). Equal volumes of lysates were either added to 5× sample buffer or incubated with no antibody, anti-gH/gL E1D1 monoclonal antibody, or anti-gp42 F-2-1 monoclonal antibody and rotated at 4° C. for at least 1 h. Agarose beads cross-linked to protein G (Amersham Biosciences) were incubated with lysates at 4° C. for at least 1 h and used to pull down IgG complexes by centrifugation. Samples were washed at least three times with complete lysis buffer and 100 μl of 2×SDS sample buffer added. Samples of whole-cell lysate and immunoprecipitate were run on 12.5% or 10% Criterion tris-HCl gels (Bio-Rad) at 120 V for 110 min followed by transfer at 90 V for 90 min to Immobilon-P transfer membranes (Millipore). Western blots immunodetection of gp42 were carried out using anti-gp42 antibody serum PB1114 as previously described (Silva et al., 2004, J. Virol. 78:5946-56, incorporated by reference herein in its entirety).

Fluorescence Polarization. A Beacon 2000 instrument (Invitrogen) was used to measure the fluorescence polarization signal that occurs when FITC-labeled gp42-derived peptide binds to soluble gH/gL. Samples were made in parallel in 100 μl volumes using 10-fold serial dilutions of protein and peptides, with subdivisions in between. To reduce nonspecific interactions and reduce protein losses at low concentrations, samples contained 0.1% tween-20 detergent. To reduce pipetting errors, parallel samples were mixed in individual tubes (Kimble Glass) and prepared identically using the same volumes for each dilution. Samples were allowed to incubate at room temperature for at least 20 min before measurement. For competition assays, the two competitors were mixed together (FITC-labeled peptide and competitor protein or peptide), and then soluble gH/gL was added last. Data were collected at 25° C.

Results

Mutants of gp42 N-terminal region. Mutants of gp42 were engineered to span the N-terminal region from residues 30 to 96 (FIG. 1A). Initially, six point mutants were made to substitute alanine for charged residues or tryptophan (FIG. 1A, bold amino acids). Since none of these mutants dramatically altered fusion, a more systematic approach was employed to remove 5 contiguous residues throughout the N-terminal region from amino acids 32 to 96 (FIG. 1A). Cell surface expression of gp42 mutants was similar to wild type gp42 in transfected CHO cells as shown by CELISA (FIG. 1B line graph). The mutants were tested for their ability to mediate membrane fusion using CHO cells transfected with gH, gL, gB, and mutant or wild-type gp42 and overlaid with B cells. Mutants with 5 -residue deletions between residues 37-56 or 72-96 showed significantly reduced membrane fusion activity, less than 25% of wild-type (FIG. 1B bar graph). In contrast, deletion of residues 57-61 or 62-66 showed only moderate reduction in membrane fusion activity to ˜50% of wild-type gp42. Deletion mutant d67-71 averaged between 25% and 50% of wild-type fusion. These data suggest that there are two functional regions within the gp42 N-terminus that we designate N-terminal region 1 (NT1) for residues 37-56 and N-terminal region 2 (NT2) for residues 67-96.

Representative western blotting of lysates immunoprecipitated with anti-gp42 mouse monoclonal antibody demonstrated the expression and size of mutant gp42 protein is nearly the same as wild-type gp42, except for the deletion mutants d62-66 and d92-96, where two and one, respectively, potential glycosylation sites were removed (FIG. 2B and data not shown). Loss of the glycosylation sites did not affect the ability of the d62-66 mutant to trigger fusion, although the d92-96 mutant was unable to mediate fusion (FIG. 1B). This may indicate that glycosylation, at least at the second site, may be important for gp42 function. This would be in contrast to HSV-1 gD in which glycosylation is not essential for function (Sodora et al., 1991, J. Virol. 65:4424-31, incorporated by reference herein in its entirety). The observation with the d92-96 mutant may also indicate another role of this region in gp42 function such as dimerization which was observed in the crystal structure (Mullen et al., 2002, Mol. Cell. 9:375-85, incorporated herein by reference in its entirety). Immunoprecipitation (IP) with anti-gH/gL E1D1 antibody followed by Western blotting for gp42 was performed to monitor gH/gL binding with gp42 (FIGS. 2A and 2B). Surprisingly, none of the deletion mutants with the exception of d45-89 was deficient in gH/gL binding as assessed by IP (representative data in FIGS. 2A and 2B and summarized in Table 1). The d45-89 mutant is not readily detected by Western blot despite surface expression confirmed by CELISA (FIG. 1B).

As an alternative approach to further understand gp42 domains required for interaction with gH/gL, more quantitative analysis was performed using CELISA experiments with 50 nM soluble gH/gL to determine gp42 mutants that retain near wild-type binding, bind at a reduced level, and completely lose binding function (FIG. 2C). Interestingly, these results did not entirely agree with the IP data (FIG. 2 and summarized in Table 1). Whereas all of the single 5-residue deletions in either NT1 or NT2 were able to bind to gH/gL in IP, one deletion mutant in NT1 and two deletions in NT2 were completely deficient in binding soluble gH/gL, while one in each category showed approximately half of wild-type binding. These results appeared to more quantitatively characterize gH/gL binding, demonstrating that some mutants at the beginning of NT1 and the end of NT2 were deficient for fusion, but were still able to bind soluble gH/gL (FIG. 2B and Table 1). Most surprisingly was the deletion mutant d57-61 which bound gH/gL in IP but did not appear to bind gH/gL in CELISA. Double deletion gp42 mutants were constructed to completely disrupt gH/gL binding since the IP results with the single deletion mutants suggested that both NT1 and NT2 are important for gp42 binding to gH/gL. Many of the double deletion mutants were similar to d45-89 in that they appeared to express well on the surface of transfected cells, they were unable to mediate membrane fusion (even lower than single deletion mutants), and some were difficult to detect in Western blots (FIGS. 1A and 2B). However, d42-46/72-76 was easily detected by Western blot and binding to gH/gL is greatly reduced (FIG. 2A). Although the deletion mutant d37-41/67-71 was not detected well by Western blot, gp42 levels in F-2-1 and E1D1 IP were often nearly similar, implying that there was more gH/gL binding than other double mutants (FIG. 2B and data not shown). However, soluble gH/gL binding to these double mutants showed little to no binding (FIG. 2C).

Peptide from gp42 residues 36 to 81 binds to soluble gH/gL with strong affinity. The gp42 mutants investigated here demonstrate that much of the N-terminal region of gp42 is critical for membrane fusion and interactions with gH/gL. Previously, it was demonstrated that a peptide corresponding to residues 36-65 binds to gH/gL with micromolar affinity, but this peptide appears to cover only one of the two N-terminal regions important for gH/gL binding (Kirschner et al., 2006, J. Virol. 80:9444-54, incorporated by reference herein in its entirety). In particular the gH/gL CELISA data indicate that residues between 67-81, but not 82-96, are important for gH/gL binding (FIG. 2C). A FITC-labeled peptide containing residues 36-81 was therefore synthesized to determine in fluorescence polarization experiments the strength of binding to soluble gH/gL. This peptide was found to bind with low nanomolar affinity with 50% binding calculated to be 5.1 nM by a nonlinear least squares fit (FIG. 3A). Compared to the gp42 peptide consisting of residues 36-65, which binds with a low micromolar K_(d), the longer 46-mer peptide gains about 500-fold affinity by extending the 30mer by 16 C-terminal amino acids to residue 81 (Kirschner et al., 2006, J. Virol. 80:9444-54, incorporated by reference herein in its entirety). This binding data is consistent with the gp42 5-residue-deletion mutants demonstrating that mutants lacking residues between 72-81 were noticeably impaired in their ability to bind soluble gH/gL (FIG. 2C). Key interaction residues exist in the N-terminal region from 36-65 (based on activity of the 36-65 peptide) and in the extended region from residue 66 and 81. These interaction regions were further investigated by studying shorter peptides.

Fluorescence polarization experiments with soluble gp42, truncated gp42-ΔN86, and short gp42-derived peptides 36-65, 36-56, 42-56, and 67-81. In order to further map the gp42 regions involved in binding to gH/gL, competition fluorescence polarization experiments were performed using 10 nM soluble gH/gL and 10 nM FITC-labeled gp42-peptide 36-81 with the addition of a competitor gp42 protein (FIG. 3B). Following the competitive reduction of the peptide polarization signal, titrations of soluble gp42 demonstrated a binding affinity for gH/gL that is very similar to that of the FITC-labeled 46-mer peptide. A nonlinear least squares fit calculated 50% inhibition of binding to be at 8.5 nM soluble gp42. Addition of peptides 36-65, 36-56, 42-56, and 67-81 revealed their relative abilities to compete with peptide 36-81 for binding to gH/gL (FIGS. 3C and 3D). Only peptides 36-65 and 42-56 were able to diminish the polarization signal, albeit at significantly higher concentrations, with 50% binding inhibition at 1.2 μM and >100 μM, respectively. Peptides 36-56 and 67-81 did not show significant binding to soluble gH/gL up to the highest concentration tested (100 μM). Compared to the low nanomolar range for soluble gp42, these short peptides have much lower affinity for gH/gL (Table 2).

TABLE 2 Activity summary of gp42-derived peptides. 50% inhibition 50% inhibition Soluble EBV 50% binding to of B-cell of epithelial gp42 residues gH/gL (nM)^(a) fusion (nM)^(b) cell fusion (nM)^(c)  33-223 8.5 — 5 36-81 5.1    ~2^(d) 5 36-65 1500 >10000 5000 36-56 >100000 >50000 >50000 42-56 ~150000 >50000 >50000 67-81 >100000 >50000 >50000 ^(a)Measured by fluorescence polarization competition experiments with 10 nM purified soluble gH/gL and 10 nM FITC-labeled gp42-peptide 36-81. ^(b)Measured by luciferase activity in fusion assay using CHO cells transfected with gH, gL, gB, addition of known concentrations of soluble gp42, and overlaid with Daudi B cells. ^(c)Measured by luciferase activity in fusion assay using CHO cells transfected with gH, gL, gB, and overlaid with 293-T epithelial cells. ^(d)Measured using lowest gp42 concentration tested.

The binding kinetics for FITC-labeled gp42-derived peptide 36-81 and soluble gH/gL were also studied. Fluorescence polarization measurements were taken at 30 s time-points after mixing 10 nM peptide and 10 nM soluble gH/gL (FIG. 4A). Maximum binding signal was achieved by 10 min, and the nonlinear least squares exponential fit for one-site binding shows a binding rate of 0.908±0.039 min⁻¹. For dissociation experiments, excess soluble gp42 was added to preincubated 10 nM peptide and 10 nM soluble gH/gL. Time-points measured over 2 h were fit to an exponential dissociation curve with a calculated half-life of the gH/gL/peptide complex at 9.86±0.6 min (FIG. 4B). A control sample with 1 μM soluble gp42-ΔN86 added to 10 nM peptide and 10 nM soluble gH/gL did not show any peptide dissociation (FIG. 4B).

Peptide from gp42 residues 36-81 is an efficient inhibitor of EBV-mediated membrane fusion. Previous work with the 36-65 peptide revealed that it acted as an inhibitor of EBV-mediated epithelial cell membrane fusion in a dose-dependent manner in the low micromolar range (Kirschner et al., 2006, J. Virol. 80:9444-54, incorporated by reference herein in its entirety). This finding is consistent with the 36-65 peptide's ability to inhibit the 36-81 peptide binding in the polarization assay. Since the longer 36-81 peptide bound gH/gL with much higher affinity than the 36-65 peptide, the 36-81 peptide was also tested for inhibition of cell fusion. As shown in FIG. 5A, the 36-81 peptide is a significantly stronger inhibitor of epithelial cell fusion with an apparent EC₅₀ of approximately 5 nM. Both soluble gp42 and the 36-81 peptide had a very similar inhibitory effect over comparable concentration ranges on epithelial cell membrane fusion [FIG. 5A in (Kirschner et al., 2006, J. Virol. 80:9444-54, incorporated by reference herein in its entirety)]. Further testing of the peptide in fusion assays with B cells revealed that the long peptide is also capable of inhibiting membrane fusion. With CHO cells transfected with gH, gL, gB, and gp42, the degree of inhibition is ˜25% of the control, which is a significant amount (p-value <0.05) as determined by Student's T-test (FIG. 5B). This decrease in fusion is modest and likely attributable to difficulties in competing the membrane-bound gH/gL/gp42 complexes, which form over 12 h transfection incubation. A significant amount of preformed gH/gL/gp42 complexes likely remain intact after incubating the peptide with the CHO cells for only 10 min before overlaying target B cells, especially as the half-life for dissociation is approximately 10 min, based on the peptide polarization results. Even greater inhibition of B-cell fusion was observed when the peptide was allowed to incubate for longer times (data not shown). To examine direct competition between gp42 and the peptide for binding cell-associated gH/gL, the B cell fusion assay was performed using known concentrations of soluble gp42 added to CHO cells transfected with gH, gL, and gB. A clear dose-dependent inhibitory effect on B cell fusion is observed when peptide and soluble gp42 compete for binding gH/gL on the same timescale (FIG. 5C). The data show a logical trend that as more soluble gp42 is added more peptide is needed to inhibit fusion. Soluble gp42 and the 46-mer peptide are competitive in the same concentration ranges, suggesting their binding affinities for gH/gL are similar.

Complementation assays with peptides and gp42-deletion mutants. The membrane fusion assay was used to test if B-cell fusion with nonfunctional gp42-deletion mutants could be rescued by adding gp42-derived peptides in trans. First the soluble truncated gp42-ΔN86 protein was added along with the longest gp42-derived peptide (residues 36-81), but no membrane fusion occurred (data not shown). This lack of fusion was observed with or without transfected gp350 that might provide more favorable contacts between the fusion proteins and the target B cell (data not shown).

Next, the short gp42-derived peptides spanning residues 36-56, 42-56, and 67-81 were tested for the ability to inhibit epithelial cell fusion. Based on their inability to block 36-81 binding in the polarization assay, we did not expect the peptides to block fusion, and indeed no inhibitory activity was detected up to 50 μM final peptide concentration (FIG. 6A). The peptides were also added in combination to see if their inhibitory effects would become apparent at micromolar concentrations, but none of these three peptides exhibited any activity when added simultaneously. However, using the peptide derived from residues 36-65, which has an inhibitory effect on epithelial cell fusion in the low micromolar range in combination with the peptide from residues 67-81, consistently enhanced inhibition was not observed, although the effect was still moderate and required peptide concentrations in the low micromolar range (FIG. 6B). Simultaneous addition of peptides spanning residues 36-65 and 67-81 in the low micromolar range did not inhibit as strongly as the single peptide spanning residues 36-81 used in the nanomolar range, indicating that their covalent linkage is important for full binding and inhibition activity.

Subsequently, the reverse experiments were performed to see if the short peptides could complement gp42-deletion mutants deficient in membrane fusion activity. Data were collected from the cell-cell fusion assay using CHO cells transfected with gH, gL, gB, and mutant gp42 (5-residue and longer deletions) and micromolar concentrations of short peptides were added immediately before overlay with B cells (FIG. 6C). Fusion assay data revealed that these short N-terminal gp42 peptides added in trans could not restore the function of gp42-deletion mutants that lost the ability to trigger fusion with B cells. The longest peptide from gp42 residues 36-81, which has nanomolar binding to gH/gL, was unable to rescue membrane fusion with any of the gp42 mutants, including the gp42 mutant lacking residues 45-89. These data indicate that the co-localization of the gp42 C-terminal lectin domain with N-terminal-gp42/gH/gL complexes is important for full fusogenic activity.

EBV infection assay with gp42-derived peptide 36-81. In order to test the effect of peptide 36-81 on entry of the whole virus, epithelial cells were infected by GFP-expressing EBV, which was produced by Akata cells. Virus was preincubated with 20 nM concentration of anti-gH/gL antibody E1D1, soluble gp42, or peptide 36-81 for 24 h at 37 C prior to a 1-h spin infection of cells in a 96-well format. The effect of peptide 36-81 on the infection of epithelial cells by EBV was measured by FACS analysis. Each of the three experimental conditions showed a reduction of infection to approximately 25% of the uninhibited EBV control (FIG. 7). These data demonstrate that a low nanomolar concentration of peptide 36-81 is able to inhibit the intact virus from entering epithelial cells, consistent with observations made in the cell-cell fusion assays.

Discussion

N-terminal deletion mutants of gp42 lose the ability to function in membrane fusion. The deletion of 5-residue segments within the N-terminus of gp42 did not substantially affect protein expression levels compared to wild-type. Membrane fusion experiments with B cells demonstrated that some mutants retain near wild-type fusion function, some allow moderate levels of fusion, and some are inactive in fusion. These deletion mutants reveal that residues 37-56 and 72-96 are absolutely required functional regions of the N-terminus of gp42 to trigger fusion, and suggest that some of the residues within 67-71 are also required (FIG. 1B). The gp42 mutants defective in membrane fusion can be rescued by the addition of soluble gp42 in the fusion assay, but not with any gp42-derived peptides that span the regions deleted (FIG. 6C). Thus, there is a requirement for direct linkage between a gp42 lectin domain (residues 111 to 217) and the N-terminal gH/gL binding site to be within the same molecule.

CELISA with gp42 5-residue deletion mutants quantitatively measures binding to soluble gH/gL. The loss of membrane fusion activity for some gp42 mutants may be due to a lack of binding to gH/gL, or to deletion of gp42 residues otherwise important for fusion activation. To investigate this hypothesis, a gH/gL-based CELISA was employed in addition to IP, and the data revealed that some defective gp42 mutants are similar to wild-type gp42 in binding gH/gL, some show moderately diminished binding, and some completely lose any interaction with gH/gL. Correlating the ability of mutants to function in membrane fusion with the ability to bind soluble gH/gL reveals mutants in there categories (see Table 1): (1) inconsequential mutants remaining fully functional, (2) loss of fusion but maintenance of wild-type gH/gL binding, (3) reduced or complete loss of fusion due to altered binding to gH/gL. Category 1 mutants are innocuous deletions and/or single substitutions that have no major effect on gp42 or gH/gL function. The deletion mutant d57-61 appears to lack gH/gL binding in the CELISA assay, but could cause fusion. However, there are a few discrepancies between the IP data and CELISA measurements for the gp42 mutants binding to gH/gL. These differences may be due to possible interactions gp42 may have with transfected gH/gL during protein expression and folding, possibly within their membrane spanning domains.

Deletion mutant d57-61 is able to promote near wild-type membrane fusion but completely loses binding to soluble gH/gL as detected in CELISA. This is a peculiar mutant that was difficult to detect in Western blot even though surface expression levels were consistently higher than wild-type gp42 (FIGS. 1B and 2B). There may be a significant contribution by the unusual tetra-proline structure (residues 57-60) in binding gH/gL, but near wild-type degree of fusion is maintained in its absence. For HSV gD, which is a functional homolog for gp42, it is thought that a flexible proline-rich region becomes exposed upon receptor binding, thus activating gH/gL and gB for membrane fusion (Carfi et al., 2002, Acta Crystallogr D Biol Crystallogr 58:836-8; Cocchi et al., 2004. Proc Natl Acad Sci USA 101:7445-50; Fusco et al., 2005, Proc Natl Acad Sci USA 102:9323-8; and Krummenacher et al., 2005, Embo J. 24:4144-53, the contents of which are incorporated by reference herein in their entireties). It was reasoned that the N-terminal region of gp42 might play an analogous role, and that for gp42 the presence of the tetra-proline motif might enable a gH/gL-dependent regulation of the gp42-N-terminal peptide. In this scenario, the deletion mutant d57-61 might be capable of activating gB-dependent fusion in the absence of gH/gL. However, fusion assays revealed that the d57-61 mutant is not capable of membrane fusion without gH/gL, i.e., transfected gB and the d57-61 mutant does not cause membrane fusion (data not shown). An alternative possible explanation for the d57-61 mutant is that it still binds gH/gL but with a lower affinity and significantly increased dissociation rate. As a preliminary test for altered binding kinetics, preformed E1D1-gH/gL complexes (500 nM E1D1 and 50 nM gH/gL) were tested in CELISA for binding d57-61, but no binding was detected even though the antibody complex is bivalent (data not shown). However, when the gp42-d57-61 mutant is transfected instead of wild-type gp42 in membrane fusion assays with B cells, the 36-81 peptide inhibits fusion somewhat more efficiently (data not shown). These data suggest that the d57-61 mutant does form complexes with gH/gL, albeit with lower binding affinity compared to wild-type gp42, and that this complex can be dissociated by adding peptide 36-81.

Interestingly, category 2 mutants that are at the beginning of NT1 and the end of NT2 are able to bind soluble gH/gL in the gH/gL CELISA but are still unable to mediate membrane fusion (FIGS. 1B and 2, Table 1). At the N-terminus of NT1, deletion mutants d37-41 and d42-46 both appear to bind gH/gL well, but are impaired in membrane fusion. The NT1 deletion mutant d37-41 contains the cleavage site of residues 40 -42 and does not secrete soluble gp42 (data not shown), potentially indicating that soluble gp42 plays an important role in membrane fusion (Ressing et al., 2005, J. Virol. 79:841-52, incorporated by reference herein in its entirety). However, it is not clear why the deletion mutant d42-46, which can bind soluble gH/gL, does not mediate fusion. Perhaps these missing residues are essential for triggering gH/gL function, even though binding to gH/gL occurs at wild-type levels. The NT2 deletion mutants d82-86, d87-91, and d92-96 were also able to bind gH/gL, but not mediate fusion. These mutants fall in or near the dimerization domain that was seen in the crystal structure of gp42:HLA-DR1 that includes residues 86-95 (Molesworth et al., 2000, J. Virol. 74:6324-32, incorporated by reference herein in its entirety). The dimerization site might therefore be important for membrane fusion, or alternatively conceivably a linker region between the gH/gL binding site and the lectin domain is required. A 5-residue insertion mutant previously studied (LI93) at this site does not affect membrane fusion, consistent with the idea that a minimal, but perhaps sequence independent, linker region is important rather than dimerization (Silva et al., 2004, J. Virol. 78:5946-56, incorporated by reference herein in its entirety). The d82-86 mutant had very low levels of fusion and these residues link the end of the gH/gL binding domain to the putative dimerization site. Further studies are required to determine whether specific sequences, dimerization or simply linker residues, are required for gp42 function in these regions of NT1 and NT2. For example, it is possible that 5-residue deletions between 82-96 primarily result in a loss of fusion function due to altered geometry of the lectin domain relative to gH/gL in the complex. These residues may act as a linker between the gH/gL binding site and the lectin domain, providing needed flexibility for the fusion process to proceed. Nevertheless, category 3 mutants reveal the “core” gp42 residues that interact with gH/gL. These residues are important for binding soluble gH/gL and essential for membrane fusion function (FIG. 1A).

The gp42-derived peptides directly bind to gH/gL. Fluorescence polarization experiments reveal that the FITC-labeled gp42-derived peptide from residues 36-81 binds to gH/gL with high affinity. This direct measurement allows quantitative data to be gathered on the binding. Both binding at equilibrium and kinetics of binding were studied. The measured values for the on-rate and off-rate of FITC-labeled 36-81 peptide binding to soluble gH/gL are consistent with values obtained in equilibrium binding experiments. The affinity of the 36-81 peptide for gH/gL was found to be nearly equivalent to the binding affinity of soluble gp42 protein. Thus, the residues sufficient for wild-type-level binding to gH/gL appear to be present in the 46-mer peptide. Additional competition experiments with shorter peptides showed significantly weaker binding affinities. Peptide from residues 36 -65 competes in the low micromolar concentration range, while the peptide from residues 42-56 just begins binding soluble gH/gL in the mid-micromolar range, confirming that the minimum residues required for high affinity gH/gL binding cover a large residue range (Table 2).

Peptides derived from gp42 inhibit epithelial cell fusion. Membrane fusion studies investigating the effect of soluble gp42 and peptides derived from the N-terminal region of gp42 revealed that they can effectively inhibit epithelial cell fusion. The soluble gp42 protein and the long 36-81 peptide inhibit in the low nanomolar range, the 36-65 peptide inhibits in the low micromolar range, and the shorter peptides do not show inhibition up to 50 μM. Nevertheless, a synergistic effect was found when adding peptides 36-65 and 67-81 in the low micromolar range, somewhat enhancing the inhibitory effect compared to 36-65 alone. The small synergistic effect of 36-65 and 67-81 peptides suggests that these segments bind with an extended peptide binding site on gH/gL, which exhibits only mild cooperativity in binding. The fact that the longer 36-81 peptide gains nearly 1000-fold binding affinity and concentration for 50% inhibition compared to the shorter peptides demonstrates the importance of having these two binding regions within a single peptide chain. Given that gp42 and gp42-derived peptides function by binding to gH/gL, it can be inferred that the inhibitory mechanism is either blockage of a critical binding site on gH/gL, such as an interaction of gH/gL with a gH/gL-receptor, or inhibition or induction of a conformational change in gH/gL rendering it unable to mediate fusion.

Peptide from gp42 residues 36-81 inhibits B cell fusion when competing with soluble gp42. The long peptide from gp42 residues 36-81 binds soluble gH/gL with approximately the same affinity as the soluble protein gp42. This suggests their activities in membrane fusion may be in the same functional range, namely the low nanomolar concentration. Indeed, when tested in direct competition with soluble gp42, the 36-81 peptide is able to inhibit B-cell fusion when its concentration is above that of soluble gp42. However, membrane fusion with B-cells proceeds only when the N-terminal region of gp42 is connected to the lectin domain, which engages the MHC class II receptor. B-cell fusion did not occur in experiments with the peptide 36-81 and soluble gp42-ΔN86 added together (data not shown). Therefore, membrane fusion requires the combination of the N-terminal region of gp42 occupying the gH/gL binding site and the same protein's proximal C-type lectin domain engaging the MHC class II receptor. In addition, none of the short gp42-derived peptides (36-56, 42-56, 67-81) has any inhibitory effect on B-cell or epithelial cell fusion, testing even at 50 μM peptide. Moreover, none of the gp42-derived peptides can rescue B cell fusion with transfected 5-residue gp42 deletion mutants. Nevertheless, the gp42 residues in this region are critical for binding to gH/gL and triggering membrane fusion. It remains unclear why the presence of these residues is insufficient to stimulate membrane fusion, even when the high affinity peptide 36-81 and the gp42-ΔN86 protein are present.

Peptide 36-81 inhibits epithelial cell infection by whole virus. Since peptide 36-81 inhibited EBV-mediated epithelial cell fusion in the low nanomolar range, its ability to inhibit intact virus infection of epithelial and B cells was examined. For epithelial cell infections, virus was produced by Akata cells, which are thought to make virus with lower levels of gp42 that is therefore more efficient at infecting epithelial cells. At a concentration of 20 nM, which is approximately four times the EC₅₀ for inhibiting epithelial cell fusion, the peptide acts similarly to anti-gH/gL antibody E1D1 and soluble gp42, reducing the infection to nearly one-quarter of the uninhibited control (FIG. 7). The peptide inhibits intact virus as effectively as it inhibits epithelial cell membrane fusion in the virus-free cell-cell fusion assay. Since the peptide is known to bind directly to gH/gL in competition for gp42, the infection assay data strongly suggest that the peptide is capable of binding gH/gL on the intact virus surface to inhibit its ability to enter epithelial cells.

In contrast, when peptide 36-81 was examined in a B-cell infection assay, using virus produced by B95-8 cells, it did not demonstrate binding (data not shown). This was likely due to the presence of higher concentrations of viral gp42 forming tight membrane-bound gH/gL/gp42 complexes, in which gp42 could not be displaced by the peptide. This finding is consistent with the results observed for peptide inhibition of B-cell membrane fusion in which even high concentrations of peptide could achieve only a modest decrease in cell-cell fusion when transfected gp42 was present (FIG. 5B). Design of other peptide or peptidomimetics might reveal a better inhibitor of viral entry into B-cells.

Characterization of the gp42 residues important for gH/gL-mediated membrane fusion. The gp42 residues found to primarily contribute to binding gH/gL (47-61 and 67-81) contain 7 prolines, 10 charged residues, and 3 aromatic residues. Other residues important for triggering fusion function, are hydrophobic (37-46) and mostly neutral (82-96). However, there are putative glycosylation sites that suggest these regions are not likely to mediate direct protein-protein interactions. In addition, gp42 has a cleavage site from residues 40-42 and a possible dimerization or linker region from residues 86-95. A crystal structure of the N-terminal region of gp42 and the structure of the gH/gL complex may provide a more complete understanding of this herpesvirus membrane fusion mechanism.

Based on the data gathered using the gp42-derived peptide 36-81 in vitro and in cell-based assays, a model of its inhibition of EBV-mediated membrane fusion is proposed (FIG. 8). Contacts mimicking gp42 are retained and membrane fusion is inhibited when bound to gH/gL.

The peptide derived from residues 36-81 acts as a low nanomolar inhibitor of B cell membrane fusion and it is as potent as gp42 at inhibiting epithelial cell membrane fusion. This peptide proves useful for future drug development to treat EBV-mediated diseases of both B and epithelial cell origin. The gp42-derived peptides, and others like it, provide new tools for studying herpesvirus entry and designing effective therapeutics.

In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different compositions and method steps described herein may be used alone or in combination with other compositions and method steps. It is to be expected that various equivalents, alternatives and modifications are possible. 

1. A pharmaceutical composition for treating Epstein-Barr virus (EBV) infection, the composition comprising: (a) a carrier; and (b) a polypeptide, or an active peptidomimetic thereof, the polypeptide comprising an amino acid sequence of EBV gp42 from about amino acids 36-81, wherein the polypeptide inhibits EBV-mediated membrane fusion with B-cells and EBV-mediated membrane fusion with epithelial cells.
 2. The composition of claim 1, wherein the polypeptide inhibits at least about 50% of EBV-mediated membrane fusion with B-cells at a concentration of less than about 100 nm.
 3. The composition of claim 1, wherein the polypeptide binds to gH/gL with a K_(d) of less than about 100 nm.
 4. The composition of claim 1, wherein the polypeptide is soluble.
 5. The composition of claim 1, wherein the polypeptide is not a membrane protein.
 6. The composition of claim 1, wherein the polypeptide does not comprise an amino acid sequence of EBV gp42 from about amino acids 100-223.
 7. The composition of claim 1, wherein the polypeptide does not comprise an amino acid sequence of EBV gp42 from about amino acids 82-223.
 8. The composition of claim 1, wherein the polypeptide does not comprise an amino acid sequence of EBV gp42 from about amino acids 1-30.
 9. The composition of claim 1, wherein the polypeptide does not comprise an amino acid sequence of EBV gp42 from about amino acids 1-35.
 10. The composition of claim 1, further comprising an additional pharmaceutical agent for treating EBV infection selected from the group consisting of glucocorticoids, antiviral drugs, and immunoglobulins.
 11. The composition of claim 10, wherein glucocorticoids include prednisone.
 12. The composition of claim 10, wherein antiviral drugs include acyclovir, desciclovir, ganciclovir, interferon-α, interferon-γ, adenine arabinoside, and phosphonoacetic acid.
 13. The composition of claim 10, wherein immunoglobulins include anti-EBV immunoglobulins conjugated to a therapeutic agent.
 14. A pharmaceutical composition for treating Epstein-Barr virus (EBV) infection, the composition comprising: (a) a carrier; and (b) a polypeptide fragment of EBV gp42, or an active peptidomimetic thereof, wherein the polypeptide fragment inhibits EBV-mediated membrane fusion with B-cells and EBV-mediated membrane fusion with epithelial cells and comprises a 1-30 amino acid N-terminal truncation and a 100-233 C-terminal truncation relative to full-length gp42.
 15. The composition of claim 14, wherein the polypeptide is soluble.
 16. The composition of claim 14, wherein the polypeptide is not a membrane protein.
 17. A pharmaceutical composition for treating Epstein-Barr virus (EBV) infection, the composition comprising: (a) a carrier; and (b) a polypeptide, or an active peptidomimetic thereof, the polypeptide comprising an amino acid sequence having at least 95% sequence identity to EBV gp42 amino acid sequence 36-81, wherein the polypeptide inhibits EBV-mediated membrane fusion with B-cells and EBV-mediated membrane fusion of epithelial cells.
 18. A method of treating EBV infection in a patient in need thereof, the method comprising administering the pharmaceutical composition of claim
 1. 19. The method of claim 18, wherein the patient has a disease selected from the group consisting of infectious mononucleosis, lymphoma, nasopharyngeal carcinoma, and hairy leukoplakia. 